Add --strictPropertyInitialization compiler option

Author: ahejlsberg

src/compiler/checker.ts

@@ -69,6 +69,7 @@ namespace ts {
         const allowSyntheticDefaultImports = getAllowSyntheticDefaultImports(compilerOptions);
         const strictNullChecks = getStrictOptionValue(compilerOptions, "strictNullChecks");
         const strictFunctionTypes = getStrictOptionValue(compilerOptions, "strictFunctionTypes");
+        const strictPropertyInitialization = getStrictOptionValue(compilerOptions, "strictPropertyInitialization");
         const noImplicitAny = getStrictOptionValue(compilerOptions, "noImplicitAny");
         const noImplicitThis = getStrictOptionValue(compilerOptions, "noImplicitThis");
 
@@ -22230,7 +22231,7 @@ namespace ts {
         }
 
         function checkPropertyInitialization(node: ClassLikeDeclaration) {
-            if (!strictNullChecks || node.flags & NodeFlags.Ambient) {
+            if (!strictNullChecks || !strictPropertyInitialization || node.flags & NodeFlags.Ambient) {
                 return;
             }
             const constructor = findConstructorDeclaration(node);

src/compiler/commandLineParser.ts

@@ -277,6 +277,13 @@ namespace ts {
             category: Diagnostics.Strict_Type_Checking_Options,
             description: Diagnostics.Enable_strict_checking_of_function_types
         },
+        {
+            name: "strictPropertyInitialization",
+            type: "boolean",
+            showInSimplifiedHelpView: true,
+            category: Diagnostics.Strict_Type_Checking_Options,
+            description: Diagnostics.Enable_strict_checking_of_property_initialization_in_classes
+        },
         {
             name: "noImplicitThis",
             type: "boolean",

src/compiler/core.ts

@@ -1923,7 +1923,7 @@ namespace ts {
             : moduleKind === ModuleKind.System;
     }
 
-    export type StrictOptionName = "noImplicitAny" | "noImplicitThis" | "strictNullChecks" | "strictFunctionTypes" | "alwaysStrict";
+    export type StrictOptionName = "noImplicitAny" | "noImplicitThis" | "strictNullChecks" | "strictFunctionTypes" | "strictPropertyInitialization" | "alwaysStrict";
 
     export function getStrictOptionValue(compilerOptions: CompilerOptions, flag: StrictOptionName): boolean {
         return compilerOptions[flag] === undefined ? compilerOptions.strict : compilerOptions[flag];

src/compiler/diagnosticMessages.json

@@ -3330,6 +3330,10 @@
         "category": "Message",
         "code": 6186
     },
+    "Enable strict checking of property initialization in classes.": {
+        "category": "Message",
+        "code": 6187
+    },
     "Variable '{0}' implicitly has an '{1}' type.": {
         "category": "Error",
         "code": 7005